# Hands-On-PhysicsHEAT & TEMPERATURE

## - Sensors -

For this activity you will need sevral sensors: 100 Ohm thermistor, 1N914 diode, thermocouple wire, resistance wire, AD590, LM35 or LM335. You will also need styrofoam cups, and hot and cold water. (Boiling water and ice preferred.)

Use your meter to measure the sensor outputs. Measure each sensor when placed in cups of hot, warm, and cold water. If possible, use ice water and boiling water because you know they will be near 0 °C and 100 °C. Make the water in a third cup as close as possible to half-way between your hot and cold cups.

Figure M2
Measuring Sensor Output

### Sensors to Investigate

• Thermistor: Measure the resistance of the thermistor. (Set the multimeter scale to K Ohms and connect the two leads.)

• Diode: Measure the voltage drop when current is passed through the diode. Note that one end of the diode has a black band; connect that to the red lead on your meter. Connect the other end of the diode to the black lead. Use the "diode check " scale. If your meter has this setting, it will pass a current through the diode and display the voltage drop caused by the diode.

• Thermocouple: Measure the voltage generated. You can construct a thermocouple by tightly joining two copper wires with a constantan one.

• Wire: Measure the resistance. For this use a thin wire that has several hundred ohms resistance per foot of wire. Measure its resistance on the K Ohm scale.

• AD590: This device passes a current in microamps equal to its absolute temperature in degrees Kelvin. Ice water is 273.2 °K, so when it is in ice water it passes 273.2 microamps (µA). In boiling water it lets 373.2 µA pass through. This current will go through the AD590 only if sufficient voltage is applied. So, you have to attach a battery and then measure the resulting current. Most inexpensive multimeters do not have a current scale. If yours does, use circuit A and the mA scale. Otherwise use circuit B and use the voltage scale.

Figure M3